Public and private safety communications using land mobile radio services have been growing at a steady rate. As such, it is becoming increasingly important for organizations and their respective communication systems to interoperate with one another. Interoperability between organizations includes the ability of a first organization's communication network and/or system to support a second (foreign) organization's subscriber units when subscriber units from the second organization roam into the first organization's communication network and/or system. In other words, it is important for subscriber units to have the ability to travel away from their home coverage system and into the coverage region of a foreign communication system, request services from the foreign communication system, and acquire such services.
While subscriber units currently are able to efficiently receive and use resources from foreign communication systems during normal or non-failure situations, often subscriber units, physically located in, but foreign to, a communication system (“roaming subscriber units”) miss or drop communications when a site or subsystem within the foreign communication system is in a failure mode, such as site trunking or subsystem isolation, respectively.
Without physically roaming into another communication system, subscriber units may also affiliate with subscriber groups from different systems. Subscriber units from one system may participate in the foreign system's subscriber group (i.e., a “non-native subscriber group”) efficiently during normal or non-failure situations, even though the subscriber unit is physically located in a different system. However, when the site or subsystem in which the subscriber unit is physically located experiences a failure, such as site trunking or subsystem isolation, the subscriber units affiliated with the non-native subscriber group may miss or drop communications.
One reason for missed and dropped communications is because of the lack of a comprehensive and effective method in which the subscriber unit is identified and allocated resources by the communication system during and after the communication system failure. Currently, there is no effective method to identify roaming subscriber units and assign provisional unit identification to roaming subscriber units during, or in the event of, a communication system failure. Similarly, there is no effective method for identifying and assigning provisional group identifications for non-native subscriber groups during, or in the event of, a communication system failure. In addition, there is no method to effectively request that the roaming subscriber units or non-native subscriber groups re-register with the communication system when the failure situation no longer applies, without the roaming subscriber unit or the subscriber unit affiliated with the non-native subscriber group missing or dropping communications.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are not often depicted in order to facilitate a less obstructed view of these various embodiments of the present disclosure. It will be further appreciated that certain actions and/or steps may be described or depicted in a particular order of occurrence while those skilled in the art will understand that such specificity with respect to sequence is not actually required. It will also be understood that the terms and expressions with respect to their corresponding respective regions of inquiry and study except where specific meaning have otherwise been set forth herein.